ACK policy for uplink and downlink MU PPDU

ABSTRACT

A network device is to function as a station (STA) in a Wireless Local Area Network (WLAN) that acknowledges a downlink (DL) multi-user (MU) physical layer (PHY) Protocol Data Unit (PPDU) transmitted by an access point (AP). The network device includes one or more processors that are configured to cause the network device functioning as the STA to perform operations including decoding a frame from the DL MU PPDU, determining whether an ACK Policy field of the frame is set to a binary value of ‘01’, determining whether trigger information for an uplink (UL) MU transmission has been obtained from the DL MU PPDU, and responsive to a determination that the ACK Policy filed of the frame is set to the binary value of ‘01’ and the trigger information has been obtained from the DL MU PPDU, transmitting a trigger-based immediate acknowledgement frame to the AP.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/170,044, filed Jun. 1, 2016 (issued as U.S. Pat. No. 9,762,487 onSep. 12, 2017), which claims the benefit of U.S. Provisional ApplicationNo. 62/170,018, filed Jun. 2, 2015, U.S. Provisional Application No.62/205,570, filed Aug. 14, 2015, U.S. Provisional Application No.62/257,657, filed Nov. 19, 2015, U.S. Provisional Application No.62/260,188, filed Nov. 25, 2015, and U.S. Provisional Application No.62/269,036, filed Dec. 17, 2015, which are hereby incorporated byreference.

FIELD OF INVENTION

The embodiments of the invention are related to the field of WirelessLocal Area Network (WLAN) operation. More specifically, the embodimentsof the invention relate to methods and apparatus for acknowledging aphysical layer (PHY) Protocol Data Unit (PPDU) in a multi-user (MU)transmission environment. Other embodiments are also disclosed.

BACKGROUND

Institute of Electrical and Electronics Engineers (IEEE) 802.11 is a setof physical and Media Access Control (MAC) specifications forimplementing wireless local area network (WLAN) communications. Thesespecifications provide the basis for wireless network products using theWi-Fi brand managed and defined by the Wi-Fi Alliance. Thespecifications define the use of the 2.400-2.500 GHz as well as the4.915-5.825 GHz bands. These spectrum bands are commonly referred to asthe 2.4 GHz and 5 GHz bands. Each spectrum is subdivided into channelswith a center frequency and bandwidth. The 2.4 GHz band is divided into14 channels spaced 5 MHz apart, though some countries regulate theavailability of these channels. The 5 GHz band is more heavily regulatedthan the 2.4 GHz band and the spacing of channels varies across thespectrum with a minimum of a 5 MHz spacing dependent on the regulationsof the respective country or territory.

WLAN devices are currently being deployed in diverse environments. Theseenvironments are characterized by the existence of many Access Points(APs) and non-AP stations (STAs) in geographically limited areas.Increased interference from neighboring devices gives rise toperformance degradation. Additionally, WLAN devices are increasinglyrequired to support a variety of applications such as video, cloudaccess, and offloading. Video traffic, in particular, is expected to bethe dominant type of traffic in WLAN deployments. With the real-timerequirements of some of these applications, WLAN users demand improvedperformance.

In a task group called IEEE 802.11ax, High Efficiency (HE) WLANstandardization is under discussion. The HE aims at improvingperformance felt by users demanding high-capacity and high-rateservices. The HE may support UL and DL MU simultaneous transmissions,which includes Multi-User Multiple-Input Multiple-Output (MU-MIMO) andOrthogonal Frequency Division Multiple Access (OFDMA) transmissions.

When an AP transmits a data frame to a STA during a DL MU transmission,the AP may solicit an immediate acknowledgement from the STA. Forexample, the AP may solicit an immediate acknowledgement from the STA bysetting the ACK Policy field of the data frame to a binary value of‘00’. According to current IEEE 802.11 specifications, setting the ACKPolicy field in this way solicits an immediate acknowledgement from aSTA in an SU manner.

The AP may transmit a DL MU physical layer (PHY) Protocol Data Unit(PPDU) eliciting STAs to provide acknowledgements. The STA may transmitan immediate ACK, transmit a delayed ACK, transmit the ACK in an SUmanner, and transmit the ACK in an MU manner. If multiple STAs transmitACKs using the same transmission resource (e.g., at the same time andfrequency resource), it may cause collision.

SUMMARY

The embodiments provide a method implemented by a station (STA) in aWireless Local Area Network (WLAN) to acknowledge a downlink (DL)multi-user (MU) physical layer (PHY) Protocol Data Unit (PPDU)transmitted by an access point (AP). The method includes receiving theDL MU PPDU, decoding a frame from the DL MU PPDU, where the frameincludes an indication requesting the STA to provide a trigger-basedimmediate acknowledgement, determining whether trigger information foran uplink (UL) MU transmission has been obtained from the DL MU PPDU,responsive to a determination that the trigger information has beenobtained from the DL MU PPDU, transmitting a trigger-based immediateacknowledgement frame to the AP, according to the trigger information,and responsive to a determination that the trigger information has notbeen obtained from the DL MU PPDU, refraining from transmitting thetrigger-based immediate acknowledgement frame to the AP.

The embodiments provide a network device to function as a station (STA)in a Wireless Local Area Network (WLAN), where the STA is configured toacknowledge a downlink (DL) multi-user (MU) physical layer (PHY)Protocol Data Unit (PPDU) transmitted by an access point (AP). Thenetwork device includes a Radio Frequency (RF) transceiver, a set of oneor more processors, and a non-transitory machine-readable medium havingstored therein an MU acknowledgement module, which when executed by theset of one or more processors, causes the network device, whenfunctioning as the STA, to receive the DL MU PPDU, decode a frame fromthe DL MU PPDU, where the frame includes an indication requesting theSTA to provide a trigger-based immediate acknowledgement, determinewhether trigger information for an uplink (UL) MU transmission has beenobtained from the DL MU PPDU, transmit a trigger-based immediateacknowledgement frame to the AP, according to the trigger information,in response to a determination that the trigger information has beenobtained from the DL MU PPDU, and refrain from transmitting thetrigger-based immediate acknowledgement frame to the AP in response to adetermination that the trigger information has not been obtained fromthe DL MU PPDU.

The embodiments provide a non-transitory machine-readable storage mediumhaving computer code stored therein that is to be executed by a set ofone or more processors of a network device functioning as a station(STA) in a Wireless Local Area Network (WLAN) to acknowledge a downlink(DL) multi-user (MU) physical layer (PHY) Protocol Data Unit (PPDU)transmitted by an access point (AP). The computer code, when executed bythe network device functioning as the STA, causes the network device toreceive the DL MU PPDU, decode a frame from the DL MU PPDU, where theframe includes an indication requesting the STA to provide atrigger-based immediate acknowledgement, determine whether triggerinformation for an uplink (UL) MU transmission has been obtained fromthe DL MU PPDU, transmit a trigger-based immediate acknowledgement frameto the AP, according to the trigger information, in response to adetermination that the trigger information has been obtained from the DLMU PPDU, and refrain from transmitting the trigger-based immediateacknowledgement frame to the AP in response to a determination that thetrigger information has not been obtained from the DL MU PPDU.

The embodiments provide a method implemented by an access point (AP) ina Wireless Local Area Network (WLAN) to elicit a trigger-based immediateacknowledgement from a station (STA). The method includes generatingtrigger information for an uplink (UL) multi-user (MU) transmission,generating a frame, where the frame includes an indication, where theindication requests the STA to provide a trigger-based immediateacknowledgement where the STA is to transmit a trigger-based immediateacknowledgement frame to the AP according to the trigger information ifthe trigger information is obtained by the STA and the STA is to refrainfrom transmitting the trigger-based immediate acknowledgement frame tothe AP if the trigger information is not obtained by the STA, andtransmitting a downlink (DL) MU physical layer (PHY) Protocol Data Unit(PPDU) to the STA, where the DL MU PPDU includes the frame and thetrigger information.

The embodiments provide a network device to function as an access point(AP) in a Wireless Local Area Network (WLAN), where the AP is configuredto elicit a trigger-based immediate acknowledgement from a station(STA). The network device includes a Radio Frequency (RF) transceiver, aset of one or more processors, and a non-transitory machine-readablemedium having stored therein an MU acknowledgement module, which whenexecuted by the set of one or more processors, causes the networkdevice, when functioning as the AP, to generate trigger information foran uplink (UL) multi-user (MU) transmission, generate a frame, where theframe includes an indication, where the indication requests the STA toprovide a trigger-based immediate acknowledgement where the STA is totransmit a trigger-based immediate acknowledgement frame to the APaccording to the trigger information if the trigger information isobtained by the STA and the STA is to refrain from transmitting thetrigger-based immediate acknowledgement frame to the AP if the triggerinformation is not obtained by the STA, and transmit a downlink (DL) MUphysical layer (PHY) Protocol Data Unit (PPDU) to the STA, where the DLMU PPDU includes the frame and the trigger information.

The embodiments provide a non-transitory machine-readable storage mediumhaving computer code stored therein that is to be executed by a set ofone or more processors of a network device functioning as an accesspoint (AP) in a Wireless Local Area Network (WLAN) to elicit atrigger-based immediate acknowledgement from a station (STA). Thecomputer code, when executed by the network device functioning as theAP, causes the network device to generate trigger information for anuplink (UL) multi-user (MU) transmission, generate a frame, where theframe includes an indication, where the indication requests the STA toprovide a trigger-based immediate acknowledgement where the STA is totransmit a trigger-based immediate acknowledgement frame to the APaccording to the trigger information if the trigger information isobtained by the STA and the STA is to refrain from transmitting thetrigger-based immediate acknowledgement frame to the AP if the triggerinformation is not obtained by the STA, and transmit a downlink (DL) MUphysical layer (PHY) Protocol Data Unit (PPDU) to the STA, where the DLMU PPDU includes the frame and the trigger information.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that differentreferences to “an” or “one” embodiment in this specification are notnecessarily to the same embodiment, and such references mean at leastone. Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is submitted that it iswithin the knowledge of one skilled in the art to affect such feature,structure, or characteristic in connection with other embodimentswhether or not explicitly described.

FIG. 1 is a diagram illustrating operations of an MU acknowledgementprocedure, according to some embodiments.

FIG. 2A is a diagram illustrating operations of an MU acknowledgementprocedure, where a trigger frame elicits a UL MU transmission, accordingto some embodiments.

FIG. 2B is a diagram illustrating operations of an MU acknowledgementprocedure, where trigger information included in a MAC header of a dataframe elicits a UL MU transmission, according to some embodiments.

FIG. 3 is a diagram illustrating a problem that can occur during an MUacknowledgement procedure, according to some embodiments.

FIG. 4 is a diagram illustrating operations of an MU acknowledgementprocedure that utilizes a trigger-based immediate acknowledgement,according to some embodiments.

FIG. 5 is a diagram illustrating operations of an MU acknowledgementprocedure, where a Block ACK Request frame elicits an immediateacknowledgement, according to some embodiments.

FIG. 6 is a diagram illustrating operations of an MU acknowledgementprocedure, where a trigger frame elicits a UL MU transmission and aBlock ACK Request frame and an ACK Policy field of a data frame elicitan immediate acknowledgement, according to some embodiments.

FIG. 7 is a diagram illustrating a problem that can occur during an MUacknowledgement procedure, according to some embodiments.

FIG. 8 is a diagram illustrating operations of an MU acknowledgementprocedure that utilizes a trigger-based immediate acknowledgement,according to some embodiments.

FIG. 9 is a diagram illustrating operations of an MU acknowledgementprocedure, where an MU Block ACK Request frame elicits an immediateacknowledgement, according to some embodiments.

FIG. 10 is a flow diagram of a process implemented by a network devicefunctioning as a non-AP STA for acknowledging a DL MU PPDU transmittedby an AP, according to some embodiments.

FIG. 11 is a flow diagram of a process implemented by a network devicefunctioning as an AP for eliciting a trigger-based immediateacknowledgement from a STA, according to some embodiments.

FIG. 12 is a block diagram of a network device implementing a STA or APthat executes an MU acknowledgement process and module, according tosome embodiments.

FIG. 13 is a block diagram of a WLAN, according to some embodiments.

FIG. 14 is a schematic block diagram exemplifying a transmitting signalprocessor in a WLAN device, according to some embodiments.

FIG. 15 is a schematic block diagram exemplifying a receiving signalprocessing unit in the WLAN, according to some embodiments.

FIG. 16 is a timing diagram providing an example of the Carrier SenseMultiple Access/Collision Avoidance (CSMA/CA) transmission procedure,according to some embodiments.

FIG. 17 is a diagram illustrating a DL MU PPDU and UL MU PPDU exchange,according to some embodiments.

DETAILED DESCRIPTION

The embodiments disclosed herein provide methods and apparatus foracknowledging a physical layer (PHY) Protocol Data Unit (PPDU) in amulti-user transmission environment. An embodiment is a methodimplemented by a station (STA) in a Wireless Local Area Network (WLAN)that utilizes the concept of a trigger-based immediate acknowledgementto acknowledge a downlink (DL) multi-user (MU) PPDU transmitted by anaccess point (AP). With a trigger-based immediate acknowledgement, a STAthat successfully decodes trigger information for an uplink (UL) MUtransmission from a DL MU PPDU transmitted by an AP transmits anacknowledgement frame to the AP in an MU manner during the UL MUtransmission, according to the trigger information (e.g., using anallocated transmission resource). On the other hand, a STA that fails tosuccessfully decode trigger information from a DL MU PPDU transmitted byan AP refrains from transmitting an acknowledgement frame to the AP (atleast until after the UL MU transmission has finished). Otherembodiments are also described and claimed.

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures and techniques have not been shown in detail inorder not to obscure the understanding of this description. It will beappreciated, however, by one skilled in the art that the invention maybe practiced without such specific details. Those of ordinary skill inthe art, with the included descriptions, will be able to implementappropriate functionality without undue experimentation.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

In the following description and claims, the terms “coupled” and“connected,” along with their derivatives, may be used. It should beunderstood that these terms are not intended as synonyms for each other.“Coupled” is used to indicate that two or more elements, which may ormay not be in direct physical or electrical contact with each other,co-operate or interact with each other. “Connected” is used to indicatethe establishment of communication between two or more elements that arecoupled with each other. A “set,” as used herein refers to any positivewhole number of items including one item.

An electronic device stores and transmits (internally and/or with otherelectronic devices over a network) code (which is composed of softwareinstructions and which is sometimes referred to as computer program codeor a computer program) and/or data using machine-readable media (alsocalled computer-readable media), such as non-transitory machine-readablemedia (e.g., machine-readable storage media such as magnetic disks,optical disks, read only memory, flash memory devices, phase changememory) and transitory machine-readable transmission media (also calleda carrier) (e.g., electrical, optical, radio, acoustical or other formof propagated signals—such as carrier waves, infrared signals). Thus, anelectronic device (e.g., a computer) includes hardware and software,such as a set of one or more processors coupled to one or morenon-transitory machine-readable storage media (to store code forexecution on the set of processors and data) and a set of one or morephysical network interface(s) to establish network connections (totransmit code and/or data using propagating signals). Put another way, atypical electronic device includes memory comprising non-volatile memory(containing code regardless of whether the electronic device is on oroff) and volatile memory (e.g., dynamic random access memory (DRAM),static random access memory (SRAM)), and while the electronic device isturned on that part of the code that is currently being executed iscopied from the slower non-volatile memory into the volatile memory(often organized in a hierarchy) for execution by the processors of theelectronic device.

A network device (ND) is an electronic device that communicativelyinterconnects other electronic devices on the network (e.g., othernetwork devices, end-user devices). Some network devices are “multipleservices network devices” that provide support for multiple networkingfunctions (e.g., routing, bridging, switching, Layer 2 aggregation,session border control, Quality of Service, and/or subscribermanagement), and/or provide support for multiple application services(e.g., data, voice, and video). Network devices or network elements caninclude APs and non-AP STAs in wireless communications systems such as awireless local area network (WLANs). STAs are devices connected to andcommunicating in a WLAN including client or user devices that connect tothe WLAN via APs. APs are network devices that may be specializedwireless access points that can communicate with other network devicesin the WLAN via the wireless medium or via wired connections. A STA orAP may be referred to herein as a WLAN device.

Conventionally, when a WLAN device (e.g., STA or AP) transmits a dataframe to another WLAN device, the transmitting WLAN device may indicateits desired acknowledgement policy in the data frame. For example, a2-bit ACK Policy subfield in the QoS Control field (e.g., bit 5 and bit6 of the QoS Control field) of a data frame can be used for thispurpose. Table 1 shows how the ACK Policy subfield may be interpreted bya WLAN device.

TABLE 1 Bits in QoS Control field Bit 5 Bit 6 Meaning Normal ACK orImplicit BAR 0 0 The addressed recipient returns an ACK or a Block ACKframe No ACK 1 0 The addressed recipient takes no action upon receipt ofthe frame No explicit acknowledge or Power Save Multi-Poll (PSMP) ACK 01 When bit 6 of the Frame Control field is set to 1: No data When bit 6of the Frame Control field is set to 0: PSMP ACK Block ACK 1 1 Theaddressed recipient takes no action upon the receipt of the frame exceptfor recording the state. The recipient can expect a Block ACK Requestframe in the future

In a task group called Institute of Electrical and Electronics Engineers(IEEE) 802.11ax, High Efficiency (HE) WLAN standardization is underdiscussion. The HE aims at improving performance felt by users demandinghigh-capacity and high-rate services. The HE may support UL and DL MUsimultaneous transmissions, which includes Multi-User Multiple-InputMultiple-Output (MU-MIMO) and Orthogonal Frequency Division MultipleAccess (OFDMA) transmissions.

When an AP (e.g., High Efficiency (HE) AP) transmits a data frame to aSTA (e.g., High Efficiency (HE) STA) during a DL MU transmission, the APmay elicit an immediate acknowledgement from the STA. For example, theAP may elicit an immediate acknowledgement from the STA by setting theACK Policy field of the data frame to a binary value of ‘00’. Accordingto current IEEE 802.11 specifications, setting the ACK Policy field inthis way elicits an immediate acknowledgement from a STA in an SUmanner.

Each payload within a DL MU PPDU transmitted by an AP during a DL MUtransmission may include a trigger frame that includes triggerinformation for a UL MU transmission. The trigger information mayinclude information regarding the UL MU transmission such as thetransmission length of the UL MU transmission and the allocation oftransmission resources for the UL MU transmission. The presence of atrigger frame in a DL MU PPDU elicits the UL MU transmission. The STAsthat successfully decode trigger information included in a trigger framemay transmit an acknowledgement frame (e.g., ACK frame or Block ACK (BA)frame) to the AP in an MU manner during the UL MU transmission,according to the trigger information (e.g., using the transmissionresource assigned to the STA).

However, if a STA fails to successfully decode the trigger information,that STA may transmit an acknowledgement frame in an SU manner, whichmay cause collisions with other acknowledgement frames transmitted byother STAs during the UL MU transmission.

Embodiments overcome the disadvantages of existing techniques byintroducing a new type of acknowledgement policy referred to herein as atrigger-based immediate acknowledgement. With a trigger-based immediateacknowledgement, a STA that successfully decodes trigger information fora UL MU transmission from a DL MU PPDU transmitted by an AP transmits anacknowledgement frame to the AP in an MU manner during the UL MUtransmission, according to the trigger information (e.g., using anallocated transmission resource). On the other hand, a STA that fails tosuccessfully decode trigger information from a DL MU PPDU transmitted byan AP refrains from transmitting an acknowledgement frame to the AP (atleast until after the UL MU transmission has finished). In this way, aSTA that fails to successfully decode trigger information from the DL MUPPDU will avoid transmitting an acknowledgement frame in an SU mannerduring the UL MU transmission, and thereby avoid causing collisions withacknowledgement frames transmitted by other STAs during the UL MUtransmission.

FIG. 1 is a diagram illustrating operations of an MU acknowledgementprocedure, according to some embodiments. For illustration purposes, theoperations in this diagram and other diagrams will be described in thecontext of a simple WLAN that includes an AP and at least two STAs(e.g., STA1 and STA2). It should be understood, however, that theprinciples and concepts described herein are not limited thereto. Inthis diagram and some of the other diagrams (FIGS. 2-9), the horizontaldimension represents the time dimension, while the vertical dimensionrepresents the frequency dimension. The AP transmits a data frame toeach of STA1 and STA2 during a DL MU transmission (e.g., in a DL MUPPDU—which may be a DL OFDMA PPDU). The data frame intended for STA1 istransmitted in a first 20 MHz sub-channel and the data frame intendedfor STA2 is transmitted in a second 20 MHz sub-channel. The data frameintended for STA1 includes an ACK Policy field that is set to indicatean Implicit Block ACK Request acknowledgement policy (e.g., ACK Policyfield is set to a binary value of ‘00’), which elicits an immediateacknowledgement from STA1. The data frame intended for STA2 includes anACK Policy field that is set to indicate a Block ACK acknowledgementpolicy (e.g., ACK Policy field is set to a binary value of ‘11’), whichsolicits a delayed acknowledgement from STA2. With a Block ACKacknowledgement policy, STA2 can expect a Block ACK Request frame fromthe AP in the future and STA2 can transmit an acknowledgement frame tothe AP in response to receiving the Block ACK Request frame from the AP.

Since the ACK Policy field of the data frame intended for STA1 is set toindicate an Implicit Block ACK Request acknowledgement policy, STA1transmits a Block ACK frame to the AP in an SU manner. Since the ACKPolicy field of the data frame intended for STA2 is set to indicate aBlock ACK acknowledgement policy, the AP transmits a Block ACK Requestframe to STA2 and STA2 transmits a Block ACK frame in response toreceiving the Block ACK Request frame from the AP.

FIG. 2A is a diagram illustrating operations of an MU acknowledgementprocedure, where a trigger frame elicits a UL MU transmission, accordingto some embodiments. The AP transmits a trigger frame and a data frameto each of STA1 and STA2 during a DL MU transmission (e.g., in a DL MUPPDU). The trigger frame and data frame intended for STA1 aretransmitted in a first 20 MHz sub-channel and the trigger frame and thedata frame intended for STA2 are transmitted in a second 20 MHzsub-channel. The data frame intended for STA1 and the data frameintended for STA2 elicit an immediate acknowledgement from STA1 andSTA2, respectively. Each trigger frame includes trigger information fora UL MU transmission. For example, the trigger information may includescheduling information for scheduling a UL MU transmission. The presenceof the trigger frames elicits a UL MU transmission. As such, STA1 andSTA2 each transmit a Block ACK frame to the AP in an MU manner duringthe UL MU transmission (e.g., in a UL MU PPDU—which may be a UL OFDMAPPDU), according to the trigger information (e.g., using thetransmission resource assigned to the STA).

FIG. 2B is a diagram illustrating operations of an MU acknowledgementprocedure, where trigger information included in a MAC header of a dataframe elicits a UL MU transmission, according to some embodiments. TheAP transmits a data frame to each of STA1 and STA2 during a DL MUtransmission (e.g., in a DL MU PPDU), where each data frame includestrigger information in its MAC header. The data frame intended for STA1is transmitted in a first 20 MHz sub-channel and the data frame intendedfor STA2 is transmitted in a second 20 MHz sub-channel. The data frameintended for STA1 and the data frame intended for STA2 elicit animmediate acknowledgement from STA1 and STA2, respectively. The presenceof the trigger information in the MAC headers of the data frames elicitsa UL MU transmission. As such, STA1 and STA2 each transmit a Block ACKframe to the AP in an MU manner during the UL MU transmission (e.g., ina UL MU PPDU), according to the trigger information (e.g., using thetransmission resource assigned to the STA).

FIG. 3 is a diagram illustrating a problem that can occur during an MUacknowledgement procedure, according to some embodiments. The APtransmits a trigger frame and a data frame to each of STA1 and STA2during a DL MU transmission (e.g., in a DL MU PPDU). The trigger frameand data frame intended for STA1 are transmitted in a first 20 MHzsub-channel and the trigger frame and data frame intended for STA2 aretransmitted in a second 20 MHz sub-channel. Each trigger frame includestrigger information for a UL MU transmission. The presence of thetrigger frames elicits a UL MU transmission. Each data frame includes anACK Policy field that is set to indicate that an immediateacknowledgement is requested (e.g., an Implicit Block ACK Requestacknowledgement policy).

In this example, STA1 successfully receives and decodes triggerinformation included in the trigger frame (transmitted by the AP toSTA1), and thus transmits a Block ACK frame to the AP in an MU mannerduring the UL MU transmission. However, in this example, STA2 fails tosuccessfully decode trigger information included in the trigger frame(transmitted by the AP to STA2). As a result, STA2 ends up transmittinga Block ACK frame to the AP in an SU manner, which collides with theBlock ACK frame transmitted by STA1 during the UL MU transmission.Embodiments described herein address this problem by introducing theconcept of a trigger-based immediate acknowledgement. An MUacknowledgement procedure that utilizes a trigger-based immediateacknowledgement to avoid such collisions is described with reference toFIG. 4.

FIG. 4 is a diagram illustrating operations of an MU acknowledgementprocedure that utilizes a trigger-based immediate acknowledgement,according to some embodiments. The AP transmits a trigger frame and dataframe to each of STA1 and STA2 during a DL MU transmission (e.g., in aDL MU PPDU). The trigger frame and data frame intended for STA1 aretransmitted in a first 20 MHz sub-channel and the trigger frame and dataframe intended for STA2 are transmitted in a second 20 MHz sub-channel.Each trigger frame includes trigger information for a UL MUtransmission. In one embodiment, each data frame includes an indicationthat the recipient (e.g., STA1 or STA2 in this example) should provide atrigger-based immediate acknowledgement. In one embodiment, thisindication is included in an ACK Policy field of the data frame. Forexample, the ACK Policy field of the data frame may be set to a binaryvalue of ‘01’ to indicate that the recipient should provide atrigger-based immediate acknowledgement (binary value of ‘01’ isnormally used for PSMP operation, but PSMP may not be used so this valuecan be re-purposed to indicate trigger-based immediate acknowledgement).With a trigger-based immediate acknowledgement, a STA that successfullydecodes trigger information for a UL MU transmission from a DL MU PPDUtransmitted by an AP transmits an acknowledgement frame to the AP in anMU manner during the UL MU transmission, according to the triggerinformation (e.g., using an allocated transmission resource). On theother hand, a STA that fails to successfully decode trigger informationfrom a DL MU PPDU transmitted by an AP refrains from transmitting anacknowledgement frame to the AP (at least until after the UL MUtransmission has finished).

In this example, STA1 successfully receives and decodes triggerinformation included in the trigger frame (transmitted by the AP toSTA1), and thus transmits a Block ACK frame to the AP in an MU mannerduring the UL MU transmission. However, in this example, STA2 fails tosuccessfully decode trigger information included in the trigger frame(transmitted by the AP to STA2). According to a trigger-based immediateacknowledgement policy, STA2 determines whether it has successfullydecoded trigger information from the DL MU PPDU (e.g., from the triggerframe in the DL MU PPDU). In this example, STA2 determines that it hasfailed to successfully decode trigger information from the DL MU PPDU.As such, STA2 refrains from transmitting an acknowledgement frame to theAP. In this way, collisions (e.g., the collision described withreference to FIG. 3) can be avoided.

In the example described above, trigger information is included in atrigger frame in the DL MU PPDU. It should be understood, however, thattrigger information can be included in a MAC header of a data frame orelsewhere within the DL MU PPDU.

In the examples described above, an AP implicitly requested an immediateacknowledgement from a STA (e.g., by setting ACK Policy field of a dataframe). In one embodiment, an AP may explicitly request an immediateacknowledgement from a STA by transmitting a Block ACK Request frame tothe STA in a DL MU PPDU. A similar problem as described above (e.g.,collision) can also occur when a Block ACK Request frame is used torequest an immediate acknowledgement from a STA. Embodiments in whichthe Block ACK Request frame is used to request an immediateacknowledgement from a STA will now be described.

FIG. 5 is a diagram illustrating operations of an MU acknowledgementprocedure, where a Block ACK Request frame elicits an immediateacknowledgement, according to some embodiments. The AP transmits a dataframe to each of STA1 and STA2 during a DL MU transmission (e.g., in aDL MU PPDU—which may be a DL OFDMA PPDU). Each data frame has its ACKPolicy field set to indicate a Block ACK acknowledgement policy (e.g.,ACK Policy field is set to a binary value of ‘11’). The AP alsotransmits a Block ACK Request frame to STA1 during the DL MUtransmission. The Block ACK Request frame and data frame intended forSTA1 are transmitted in a first 20 MHz sub-channel and the data frameintended for STA2 is transmitted in a second 20 MHz sub-channel. TheBlock ACK Request frame elicits an immediate acknowledgement from STA1in an SU manner. As such, following the DL MU transmission, STA1transmits a Block ACK frame to the AP in an SU manner. The AP thentransmits a Block ACK Request frame to STA2, which elicits an immediateacknowledgement from STA2 in an SU manner. As such, upon receiving theBlock ACK Request frame from the AP, STA2 transmits a Block ACK frame tothe AP.

FIG. 6 is a diagram illustrating operations of an MU acknowledgementprocedure, where a trigger frame elicits a UL MU transmission and aBlock ACK Request frame and an ACK Policy field of a data frame elicitan immediate acknowledgement, according to some embodiments. The APtransmits a trigger frame, a Block ACK Request frame, and a data frameto each of STA1 and STA2 during a DL MU transmission (e.g., in a DL MUPPDU). The trigger frame, Block ACK Request frame, and data frameintended for STA1 are transmitted in a first 20 MHz sub-channel and thetrigger frame, Block ACK Request frame, and data frame intended for STA2are transmitted in a second 20 MHz sub-channel. Each trigger frameincludes trigger information for a UL MU transmission. The presence ofthe trigger frames elicits a UL MU transmission. Each data frame has itsACK Policy field set to indicate a Block ACK acknowledgement policy(e.g., ACK Policy field is set to a binary value of ‘11’). The presenceof the Block ACK Request frames in combination with the setting of theACK Policy fields of the data frames (to indicate a Block ACKacknowledgement policy) elicits an immediate acknowledgement from theSTAs. As such, each of STA1 and STA2 transmits a Block ACK frame to theAP in an MU manner during the UL MU transmission (e.g., in a UL MUPPDU—which may be a UL OFDMA PPDU), according to the trigger information(e.g., using the transmission resource assigned to the STA). In oneembodiment, a STA (e.g., STA1 or STA2) may transmit additional frames(e.g., one or more data frames) during the UL MU transmission (if timepermits).

FIG. 7 is a diagram illustrating a problem that can occur during an MUacknowledgement procedure, according to some embodiments. The APtransmits a trigger frame, a Block ACK Request frame, and a data frameto each of STA1 and STA2 during a DL MU transmission (e.g., in a DL MUPPDU). The trigger frame, Block ACK Request frame, and data frameintended for STA1 are transmitted in a first 20 MHz sub-channel and thetrigger frame, Block ACK Request frame, and data frame intended for STA2are transmitted in a second 20 MHz sub-channel. Each trigger frameincludes trigger information for a UL MU transmission. The presence ofthe trigger frames elicits a UL MU transmission. Each data frame has itsACK Policy field set to indicate a Block ACK acknowledgement policy(e.g., ACK Policy field is set to a binary value of ‘11’). The presenceof the Block ACK Request frames in combination with the setting of theACK Policy fields of the data frames (to indicate a Block ACKacknowledgement policy) elicits an immediate acknowledgement from theSTAs.

In this example, STA1 successfully receives and decodes triggerinformation included in the trigger frame (transmitted by the AP toSTA1), and thus transmits a Block ACK frame to the AP in an MU mannerduring the UL MU transmission. However, in this example, STA2 fails tosuccessfully decode trigger information included in the trigger frame(transmitted by the AP to STA2). As a result, STA2 ends up transmittinga Block ACK frame to the AP in an SU manner, which collides with theBlock ACK frame transmitted by STA1 during the UL MU transmission.Embodiments described herein address this problem by introducing theconcept of a trigger-based immediate acknowledgement. An MUacknowledgement procedure that utilizes a trigger-based immediateacknowledgement to avoid such collisions is described with reference toFIG. 8.

FIG. 8 is a diagram illustrating operations of an MU acknowledgementprocedure that utilizes a trigger-based immediate acknowledgement,according to some embodiments. The AP transmits a trigger frame, a BlockACK Request frame, and a data frame to each of STA1 and STA2 during a DLMU transmission (e.g., in a DL MU PPDU). The trigger frame, Block ACKRequest frame, and data frame intended for STA1 are transmitted in afirst 20 MHz sub-channel and the trigger frame, Block ACK Request frame,and data frame intended for STA2 are transmitted in a second 20 MHzsub-channel. Each trigger frame includes trigger information for a UL MUtransmission. In one embodiment, each Block ACK Request frame includesan indication that the recipient (e.g., STA1 or STA2 in this example)should provide a trigger-based immediate acknowledgement. In oneembodiment, this indication is included in a Block ACK Request (BAR) ACKPolicy field of the Block ACK Request frame. For example, the BAR ACKPolicy field of the Block ACK Request frame may be set to a binary valueof ‘1’ to indicate that the recipient should provide a trigger-basedimmediate acknowledgement (binary value of ‘1’ is normally used for PSMPoperation, but PSMP may not be used so this value can be re-purposed toindicate trigger-based immediate acknowledgement). Each data frame hasits ACK Policy field set to indicate a Block ACK acknowledgement policy(e.g., ACK Policy field is set to a binary value of ‘11’). With atrigger-based immediate acknowledgement, a STA that successfully decodestrigger information for a UL MU transmission from a DL MU PPDUtransmitted by an AP transmits an acknowledgement frame to the AP in anMU manner during the UL MU transmission, according to the triggerinformation (e.g., using an allocated transmission resource). On theother hand, a STA that fails to successfully decode trigger informationfrom a DL MU PPDU transmitted by an AP refrains from transmitting anacknowledgement frame to the AP (at least until after the UL MUtransmission has finished).

In this example, STA1 successfully receives and decodes triggerinformation included in the trigger frame (transmitted by the AP toSTA1), and thus transmits a Block ACK frame to the AP in an MU mannerduring the UL MU transmission. However, in this example, STA2 fails tosuccessfully decode trigger information included in the trigger frame(transmitted by the AP to STA2). According to a trigger-based immediateacknowledgement policy, STA2 determines whether it has successfullydecoded trigger information from the DL MU PPDU (e.g., from the triggerframe in the DL MU PPDU). In this example, STA2 determines that it hasfailed to successfully decode trigger information from the DL MU PPDU.As such, STA2 refrains from transmitting an acknowledgement frame to theAP. In this way, collisions (e.g., the collision described withreference to FIG. 7) can be avoided.

In the example described above, trigger information is included in atrigger frame in the DL MU PPDU. It should be understood, however, thattrigger information can be included in a MAC header of a data frame orelsewhere within the DL MU PPDU. For example, in one embodiment, triggerinformation is included in a Block ACK Request frame. Such frame isreferred to herein as an MU Block ACK Request frame (or MU-BAR frame).

FIG. 9 is a diagram illustrating operations of an MU acknowledgementprocedure, where an MU Block ACK Request frame elicits an immediateacknowledgement, according to some embodiments. The AP transmits an MUBlock ACK Request frame and a data frame to each of STA1 and STA2 duringa DL MU transmission (e.g., in a DL MU PPDU). The MU Block ACK Requestframe and data frame intended for STA1 are transmitted in a first 20 MHzsub-channel and the MU Block ACK Request frame and data frame intendedfor STA2 are transmitted in a second 20 MHz sub-channel. Each MU BlockACK Request frame includes trigger information for a UL MU transmission.Each data frame has its ACK Policy field set to indicate a Block ACKacknowledgement policy (e.g., ACK Policy field is set to a binary valueof ‘11’). The presence of the MU Block ACK Request frames elicits animmediate acknowledgement from the STAs in an MU manner. As such, eachof STA1 and STA2 transmits a Block ACK frame to the AP in an MU mannerduring the UL MU transmission (e.g., in a UL MU PPDU—which may be a ULOFDMA PPDU), according to the trigger information (e.g., using thetransmission resource assigned to the STA). In one embodiment, a STA(e.g., STA1 or STA2) may transmit additional frames (e.g., one or moredata frames) during the UL MU transmission (if time permits). In oneembodiment, an AP may transmit a Block ACK Request frame (normal non-MUBlock ACK Request frame) to a STA to elicit an immediate acknowledgementfrom the STA in an SU manner and the AP may transmit an MU Block ACKframe to a STA to elicit an immediate acknowledgement from the STA in anMU manner.

FIG. 10 is a flow diagram of a process implemented by a network devicefunctioning as a non-AP STA for acknowledging a DL MU PPDU transmittedby an AP, according to some embodiments. In one embodiment, theoperations of the flow diagram may be performed by a network devicefunctioning as non-AP STA in a wireless communications network (e.g., aWLAN). The operations in this flow diagram and other flow diagrams willbe described with reference to the exemplary embodiments of the otherfigures. However, it should be understood that the operations of theflow diagrams can be performed by embodiments of the invention otherthan those discussed with reference to the other figures, and theembodiments of the invention discussed with reference to these otherfigures can perform operations different than those discussed withreference to the flow diagrams.

In one embodiment, the process is initiated when the STA receives a DLMU PPDU from the AP (block 1010). The STA decodes a frame from the DL MUPPDU, where the frame includes an indication requesting the STA toprovide a trigger-based immediate acknowledgement (block 1020). In oneembodiment, the frame is a data frame. In one embodiment, the indicationrequesting the STA to provide a trigger-based immediate acknowledgementis included in an ACK Policy field of the frame. In one embodiment, theACK Policy field is set to a binary value of ‘01’ to request that theSTA provide a trigger-based immediate acknowledgement. In oneembodiment, the frame is a Block ACK Request frame. In one embodiment,the indication requesting the STA to provide a trigger-based immediateacknowledgement is included in a Block ACK Request (BAR) ACK Policyfield of the Block ACK Request frame. In one embodiment, the BAR ACKPolicy field is set to a binary value of ‘1’ to request that the STAprovide a trigger-based immediate acknowledgement. In one embodiment,the frame is an MU Block ACK Request frame.

The STA determines whether trigger information for a UL MU transmissionhas been (successfully) obtained (e.g., successfully decoded) from theDL MU PPDU (decision block 1030). In one embodiment, the triggerinformation for the UL MU transmission includes information regarding anallocation of transmission resources for the UL MU transmission. If theSTA determines that it has obtained trigger information from the DL MUPPDU, then the STA transmits a trigger-based immediate acknowledgementframe to the AP (e.g., during the UL MU transmission), according to thetrigger information (e.g., transmitting the trigger-based immediateacknowledgement frame by using a transmission a transmission resourceallocated to the STA) (block 1040). In one embodiment, the STA transmitsthe trigger-based immediate acknowledgement frame to the AP a shortinter frame space (SIFS) after receiving the DL MU PPDU. On the otherhand, if the STA determines that it has failed to obtain triggerinformation from the DL MU PPDU, then the STA refrains from transmittingthe trigger-based immediate acknowledgement frame to the AP (block1050). In one embodiment, if the STA determines that it has failed toobtain trigger information from the DL MU PPDU, the STA waits for aBlock ACK Request frame for the frame from the AP and transmits anacknowledgement frame for the frame to the AP in response to receivingthe Block ACK Request frame. In one embodiment, if the STA determinesthat it has failed to obtain trigger information from the DL MU PPDU,the STA transmits an acknowledgement frame to the AP during a subsequenttransmission opportunity (e.g., TXOP), before it receives a Block ACKRequest frame from the AP.

FIG. 11 is a flow diagram of a process implemented by a network devicefunctioning as an AP for eliciting a trigger-based immediateacknowledgement from a STA, according to some embodiments. In oneembodiment, the operations of the flow diagram may be performed by anetwork device functioning as an AP in a wireless communications network(e.g., a WLAN).

The AP generates trigger information for a UL MU transmission (block1105). In one embodiment, the trigger information for the UL MUtransmission includes information regarding an allocation oftransmission resources for the UL MU transmission. The AP generates aframe, where the frame includes an indication, wherein the indicationrequests the STA to provide a trigger-based immediate acknowledgementwhere the STA is to transmit a trigger-based immediate acknowledgementframe to the AP (e.g., during the UL MU transmission) according to thetrigger information if the trigger information is obtained (e.g.,successfully decoded) by the STA and the STA is to refrain fromtransmitting the trigger-based immediate acknowledgement frame to the APif the trigger information is not obtained by the STA (block 1110). Inone embodiment, the frame is a data frame. In one embodiment, theindication requesting the STA to provide a trigger-based immediateacknowledgement is included in an ACK Policy field of the frame. In oneembodiment, the ACK Policy field is set to a binary value of ‘01’ torequest that the STA provide a trigger-based immediate acknowledgement.In one embodiment, the frame is a Block ACK Request frame. In oneembodiment, the indication requesting the STA to provide a trigger-basedimmediate acknowledgement is included in a Block ACK Request (BAR) ACKPolicy field of the Block ACK Request frame. In one embodiment, the BARACK Policy field is set to a binary value of ‘1’ to request that the STAprovide a trigger-based immediate acknowledgement. In one embodiment,the frame is an MU Block ACK Request frame. The STA then transmits a DLMU PPDU to the STA, where the DL MU PPDU includes the frame and thetrigger information (block 1120).

As mentioned above, in one embodiment, trigger information can beincluded in a trigger frame in a DL MU PPDU. In one embodiment, multipleframes, including the trigger frame, can be included in a DL MU PPDU byaggregating the frames (e.g., Mac Protocol Data Units (MPDUs)) in anaggregate MPDU (A-MPDU). In one embodiment, at most one frame thatincludes trigger information can be included in the A-MPDU. In oneembodiment, the frame that includes the trigger information should bethe first frame or last frame in the A-MPDU. In one embodiment, the ACKPolicy field of other frames in the A-MPDU should not be set to indicatea Normal ACK acknowledgement policy, Implicit Block ACK Requestacknowledgement policy, or a Block ACK acknowledgement policy. The ACKPolicy field of a data frame in the A-MPDU may be set to a reservedvalue (e.g., binary value of ‘01’) to indicate that the recipient shouldprovide a trigger-based immediate acknowledgement. In this case, theacknowledgement behavior of the recipient depends on whether therecipient is able to successfully receive and decode the triggerinformation (e.g., from the trigger frame or other frame in the A-MPDU).For example, when a frame in a DL MU PPDU includes an indication thatthe recipient should provide a trigger-based immediate acknowledgement(e.g., ACK Policy field of the data frame is set to a binary value of‘01’), the acknowledgement behavior of the recipient can be as follows:

ACK Policy Set to 01: PSMP Context or UL OFDMA Context

-   In a frame that is in the PSMP context    -   i) When bit 6 of the Frame Control field is set to 1:    -   There may be a response frame to the frame that is received, but        it is neither the ACK frame nor any Data frame of        subtype+CF-ACK. The ACK Policy subfield for QoS CF-Poll and QoS        CF-ACK+CF-Poll Data frames is set to this value.    -   ii) When bit 6 of the Frame Control field is set to 0:    -   The acknowledgment for a frame indicating PSMP ACK when it        appears in a PSMP downlink transmission time (PSMP-UTT) is to be        received in a later PSMP uplink transmission time (PSMP-UTT).        The acknowledgment for a frame indicating PSMP ACK when it        appears in a PSMP-UTT is to be received in a later PSMP-DTT.-   In a frame that is in the UL OFDMA context    -   i) The addressed recipient that receives a frame having the        sub-channel assignment information returns an ACK/Block ACK        frame, either individually or as part of an A-MPDU starting a        SIFS after the PPDU carrying the frame, according to the        sub-channel assignment information specified in the received        frame.    -   ii) The addressed recipient that does not receive a frame having        the sub-channel assignment information takes no action upon the        receipt of the frame except for recording the state. The        recipient can expect a Block ACK Request frame in the future to        which it responds using the procedure described in Block        acknowledgment mechanism. But, before receiving a Block ACK        Request frame in the future, when the addressed recipient        obtains a TXOP, it can return an ACK/Block ACK frame in an        unsolicited manner. This unsolicited ACK/Block ACK frame        transmission is similar to the delayed block ACK policy. Through        the ACK Policy field, the addressed recipient knows that it is        requested to return an ACK/Block ACK frame. But, because of a        loss of the sub-channel assignment information, the addressed        recipient cannot return an ACK/Block ACK frame. So, when the        addressed recipient obtains a new TXOP later, it can return an        ACK/Block ACK frame for avoiding an unnecessary retransmission        from the AP.

As mentioned above, in one embodiment, trigger information can beincluded in a MAC header of a frame in a DL PPDU. In this case, in oneembodiment, the ACK Policy field of a data frame in the A-MPDU must beset to indicate a Normal ACK acknowledgement policy or Implicit BlockACK Request acknowledgement policy. In one embodiment, triggerinformation in the MAC header of all frames in an A-MPDU have the sameinformation. In one embodiment, when the ACK Policy field of a dataframe in the A-MPDU is set to indicate a No ACK acknowledgement policy,then a transmission resource assignment information for the recipient ofthat data frame is not included in the trigger information.

As mentioned above, in one embodiment, trigger information can beincluded in an MU Block ACK Request frame. In one embodiment, the MUBlock ACK Request frame may have the following format:

Per-User Per-User Frame Duration/ BAR Block ACK Sub-channel Control IDRA TA Control Request Assignment 2 2 6 6 2 Variable octets octets octetsoctets octets (Repeated for each user)

The BAR Control field includes the number of users from which animmediate acknowledgement is requested. The Per-User Block ACK Requestfield and the Per-User Sub-channel Assignment field is repeated for eachuser. A recipient of the Multi-User Block ACK Request frame respondswith an ACK frame or Block ACK frame that is transmitted during the ULMU transmission, according to the sub-channel assignment indicated inthe Per-User Sub-Channel Assignment field. One or more MU Block ACKRequest frames can be included in the DL MU PPDU. However, since thenormal (non-MU) Block ACK Request frame can still be used to request anACK frame or Block ACK frame that is transmitted in an SU manner, in oneembodiment, an MU Block ACK Request frame and a normal Block ACK Requestframe should not be present in the same DL MU PPDU together. An MU BlockACK Request frame can be included in an A-MPDU (with other frames). Inthis case, in one embodiment, the MU Block ACK Request frame should bethe first or last frame in the A-MPDU.

In one embodiment, at most one frame that includes trigger informationcan be included in an A-MPDU. In one embodiment, when a Block ACKRequest frame is included in an A-MPDU, the ACK Policy field of the dataframes in the A-MPDU should be set to Block ACK (since a Block ACKRequest frame is also present in the A-MPDU). In one embodiment, the BARACK Policy field of the Block ACK Request frame in the A-MPDU should notbet set to a binary value of ‘0’ (Normal ACK), but should be set to areserved value (e.g., binary value of ‘1’) to indicate that therecipient should provide a trigger-based immediate acknowledgement. Inthis case, the acknowledgement behavior of the recipient depends onwhether the recipient is able to successfully receive and decode thetrigger information (e.g., from a trigger frame or other frame in theA-MPDU). For example, when a Block ACK Request frame in a DL MU PPDUincludes an indication that the recipient should provide a trigger-basedimmediate acknowledgement (e.g., BAR ACK Policy field of the Block ACKRequest frame is set to a binary value of ‘1’), the acknowledgementbehavior of the recipient can be as follows:

BAR ACK Policy set to 1: PSMP Context or UL OFDMA Context

-   In a frame that is in the PSMP context    -   i) No Acknowledgement.    -   The addressee sends no immediate response upon receipt of the        frame. The BAR ACK Policy subfield is set to this value when the        sender does not require immediate acknowledgment. The value 1 is        not used in a basic Block ACK Request frame outside a PSMP        sequence. The value 1 is not used in a Multi-TID Block ACK        Request frame.-   In a frame that is in the UL OFDMA context    -   i) The addressed recipient that receives a frame having the        sub-channel assignment information returns an ACK/Block ACK        frame, either individually or as part of an A-MPDU starting a        SIFS after the PPDU carrying the frame, according to the        sub-channel assignment information specified in the received        frame.    -   ii) The addressed recipient that does not receive a frame having        the sub-channel assignment information takes no action upon the        receipt of the frame except for recording the state. The        recipient can expect a Block ACK Request frame in the future to        which it responds using the procedure described in Block        acknowledgment mechanism.

In one embodiment, when a Block ACK Request frame in a DL MU PPDUincludes an indication that the recipient should provide an immediateacknowledgement in SU manner (e.g., BAR ACK Policy field of the BlockACK Request frame is set to a binary value of ‘0’), the acknowledgementbehavior of the recipient can be as follows:

BAR ACK Policy Set to 0: PSMP Context or SU Context

-   In a frame that is in the PSMP context    -   i) Normal Acknowledgment.    -   The BAR ACK Policy subfield is set to this value when the sender        requires immediate acknowledgment. The addressee returns an ACK        frame (per PSMP acknowledgment rules).-   In a frame that is in the SU context    -   i) The addressed recipient returns a Block ACK frame, either        individually or as part of an A-MPDU starting a SIFS after the        PPDU carrying the frame.

In one embodiment, MU acknowledgement behavior is as follows. At mostone of the following frames can be present in an A-MPDU for eachintended recipient of a DL MU PPDU: i) one or more QoS data frames withACK Policy field set to indicate an Implicit Block ACK Requestacknowledgement policy; ii) one or more QoS data frames with ACK Policyfield set to indicate that the recipient should provide a trigger-basedimmediate acknowledgement (e.g., ACK Policy field is set to a binaryvalue of ‘01’); iii) a Block ACK Request frame; and iv) an MU Block ACKRequest frame.

In one embodiment, a DL MU PPDU should not include more than one A-MPDUthat includes one or more of the following frames that elicit animmediate acknowledgement in SU manner: i) one or more QoS data frameswith ACK Policy field set to indicate an Implicit Block ACK Requestacknowledgement policy; and ii) a Block ACK Request frame.

In one embodiment, a DL MU PPDU may include more than one A-MPDU thatincludes one or more of the following frames that elicit an immediateacknowledgement in MU manner: i) one or more QoS data frames with theACK Policy field set to indicate that the recipient should provide atrigger-based immediate acknowledgement (e.g., ACK Policy field is setto a binary value of ‘01’); and ii) an MU Block ACK Request frame.

In one embodiment, when a DL MU PPDU includes an A-MPDU that includes aQoS data frame with ACK Policy field set to indicate an Implicit BlockACK Request acknowledgement policy or a Block ACK Request frame, thenthe following frames cannot be present in the DL MU PPDU: i) one or moreQoS data frames with the ACK Policy field set to indicate that therecipient should provide a trigger-based immediate acknowledgement(e.g., ACK Policy field is set to a binary value of ‘01’); and ii) an MUBlock ACK Request frame.

In one embodiment, when the ACK Policy field of a data frame in an UL MUPPDU (transmitted from a STA to an AP) is set to indicate an ImplicitBlock ACK Request acknowledgement policy (e.g., ACK Policy field is setto a binary value of ‘00’), the AP may respond by transmitting an ACKframe or Block ACK frame to the STA in either an SU manner or MU manner(it is up to the AP to decide). This means that the acknowledgementbehavior can be different depending on the direction of transmission(e.g., UL MU transmission vs. DL MU transmission). In one embodiment,the acknowledgement behavior can be summarized as follows in Table 2:

TABLE 2 Immediate Response Immediate Response ACK Policy Type of DL MUPPDU Type of UL MU PPDU bits: 00 SU PPDU SU PPDU or MU PPDU bits: 01 MUPPDU Not allowed

In one embodiment, one or more Block ACK Request frames may be presentin an UL MU PPDU. In one embodiment, a normal (non-MU) Block ACK Requestframe included in an UL MU PPDU elicits an immediate acknowledgementfrom the AP in either an SU manner or MU manner (it is up to the AP todecide). In one embodiment, the acknowledgement behavior with respect toa Block ACK Request frame can be summarized as follows in Table 3:

TABLE 3 Block ACK Immediate Response Immediate Response Request TypeType of DL MU PPDU Type of UL MU PPDU Normal Block SU PPDU SU PPDU or MUPPDU ACK Request Multi-User Block MU PPDU Not allowed ACK Request

FIG. 12 is a block diagram of a network device implementing a STA or APthat executes an MU acknowledgement process and module, according tosome embodiments. In a wireless local area network (WLAN) such as theexample WLAN illustrated in FIG. 13, a basic service set (BSS) includesa plurality of network devices referred to herein as WLAN devices. Eachof the WLAN devices may include a medium access control (MAC) layer anda physical (PHY) layer according to IEEE 802.11 standard. In theplurality of WLAN devices, at least one WLAN device may be an AP station(e.g., access point 0 and access point 1 in FIG. 13) and the other WLANdevices may be non-AP stations (non-AP STAs), (e.g., stations 0-3 inFIG. 13). Alternatively, all of the plurality of WLAN devices may benon-AP STAs in an Ad-hoc networking environment. In general, the AP STAand the non-AP STA may be each referred to herein as a station (STA).However, for ease of description, only the non-AP STA will be referredto herein as a STA whereas the AP stations are referred to herein as APsfor ease of description. As shown in FIG. 13, a WLAN can have anycombination of STAs and APs that can form a discrete network, an ad hocnetwork or any combination thereof. Any number of APs and STAs can beincluded in a WLAN and any topology and configuration of such APs andSTAs in the network can be utilized.

The example WLAN device 1 includes a baseband processor 10, a radiofrequency (RF) transceiver 20, an antenna unit 30, memory 40, an inputinterface unit 50, an output interface unit 60, and a bus 70. Thebaseband processor 10 performs baseband signal processing, and includesa MAC processor 11 and a PHY processor 15. These processors can be anytype of integrated circuit (IC) including a general processing unit oran application specific integrated circuit (ASIC). In some embodiments,the MAC processor 11 also implements an MU acknowledgement (ACK) module1200. The MU acknowledgement module 1200 can implement the respectivefunctions for any combination of the embodiments described herein abovewith regard to FIGS. 1-13. In other embodiments, the MU acknowledgementmodule 1200 may be implemented by or distributed over both the PHYprocessor 15 and the MAC processor 11. The MU acknowledgement module1200 may be implemented as software or as hardware components of eitherthe PHY processor 15 or MAC processor 11.

In one embodiment, the MAC processor 11 may include a MAC softwareprocessing unit 12 and a MAC hardware processing unit 13. The memory 40may store software (hereinafter referred to as “MAC software”),including at least some functions of the MAC layer. The MAC softwareprocessing unit 12 executes the MAC software to implement some functionsof the MAC layer and the MAC hardware processing unit 13 may implementthe remaining functions of the MAC layer in hardware (hereinafterreferred to “MAC hardware”). However, the MAC processor 11 is notlimited to this distribution of functionality.

The PHY processor 15 includes a transmitting signal processing unit 100and a receiving signal processing unit 200 described further hereinbelow with reference to FIGS. 9 and 10.

The baseband processor 10, the memory 40, the input interface unit 50,and the output interface unit 60 may communicate with each other via thebus 70. The radio frequency (RF) transceiver 20 includes an RFtransmitter 21 and an RF receiver 22. The memory 40 may further store anoperating system and applications. In some embodiments, the memory maystore recorded information about captured frames. The input interfaceunit 50 receives information from a user and the output interface unit60 outputs information to the user.

The antenna unit 30 includes one or more antennas. When a MIMO orMU-MIMO system is used, the antenna unit 30 may include a plurality ofantennas.

FIG. 14 is a schematic block diagram exemplifying a transmitting signalprocessor in a WLAN device, according to some embodiments. Referring tothe above drawing, a transmitting signal processing unit 100 includes anencoder 110, an interleaver 120, a mapper 130, an inverse Fouriertransformer (IFT) 140, and a guard interval (GI) inserter 150. Theencoder 110 encodes input data. For example, the encoder 110 may be aforward error correction (FEC) encoder. The FEC encoder may include abinary convolutional code (BCC) encoder followed by a puncturing deviceor may include a low-density parity-check (LDPC) encoder.

The transmitting signal processing unit 100 may further include ascrambler for scrambling the input data before encoding to reduce theprobability of long sequences of 0s or 1s. If BCC encoding is used inthe encoder 110, the transmitting signal processing unit 100 may furtherinclude an encoder parser for demultiplexing the scrambled bits among aplurality of BCC encoders. If LDPC encoding is used in the encoder 110,the transmitting signal processing unit 100 may not use the encoderparser.

The interleaver 120 interleaves the bits of each stream output from theencoder to change the order of bits. Interleaving may be applied onlywhen BCC encoding is used. The mapper 130 maps the sequence of bitsoutput from the interleaver to constellation points. If LDPC encoding isused in the encoder 110, the mapper 130 may further perform LDPC tonemapping in addition to constellation mapping.

When multiple input-multiple output (MIMO) or multiple user (MU)-MIMO isused, the transmitting signal processing unit 100 may use a plurality ofinterleavers 120 and a plurality of mappers 130 corresponding to thenumber Nss of spatial streams. In this case, the transmitting signalprocessing unit 100 may further include a stream parser for dividingoutputs of the BCC encoders or the LDPC encoder into blocks that aresent to different interleavers 120 or mappers 130. The transmittingsignal processing unit 100 may further include a space-time block code(STBC) encoder for spreading the constellation points from the Nssspatial streams into NsTs space-time streams and a spatial mapper formapping the space-time streams to transmit chains. The spatial mappermay use direct mapping, spatial expansion, or beamforming.

The IFT 140 converts a block of the constellation points output from themapper 130 or the spatial mapper to a time domain block (i.e., a symbol)by using an inverse discrete Fourier transform (IDFT) or an inverse fastFourier transform (IFFT). If the STBC encoder and the spatial mapper areused, the inverse Fourier transformer 140 may be provided for eachtransmit chain.

When MIMO or MU-MIMO is used, the transmitting signal processing unit100 may insert cyclic shift diversities (CSDs) to prevent unintentionalbeamforming. The CSD insertion may occur before or after the inverseFourier transform 140. The CSD may be specified per transmit chain ormay be specified per space-time stream. Alternatively, the CSD may beapplied as a part of the spatial mapper. When MU-MIMO is used, someblocks before the spatial mapper may be provided for each user.

The GI inserter 150 prepends a GI to the symbol. The transmitting signalprocessing unit 100 may optionally perform windowing to smooth edges ofeach symbol after inserting the GI. The RF transmitter 21 converts thesymbols into an RF signal and transmits the RF signal via the antennaunit 30. When MIMO or MU-MIMO is used, the GI inserter 150 and the RFtransmitter 21 may be provided for each transmit chain.

FIG. 15 is a schematic block diagram exemplifying a receiving signalprocessing unit in the WLAN, according to some embodiments. Referring toFIG. 15, a receiving signal processing unit 200 includes a GI remover220, a Fourier transformer (FT) 230, a demapper 240, a deinterleaver250, and a decoder 260.

An RF receiver 22 receives an RF signal via the antenna unit 30 andconverts the RF signal into symbols. The GI remover 220 removes the GIfrom the symbol. When MIMO or MU-MIMO is used, the RF receiver 22 andthe GI remover 220 may be provided for each receive chain.

The FT 230 converts the symbol (i.e., the time domain block) into ablock of constellation points by using a discrete Fourier transform(DFT) or a fast Fourier transform (FFT). The Fourier transformer 230 maybe provided for each receive chain.

When MIMO or MU-MIMO is used, the receiving signal processing unit 200may use a spatial demapper for converting the Fourier transformedreceiver chains to constellation points of the space-time streams and anSTBC decoder for despreading the constellation points from thespace-time streams into the spatial streams.

The demapper 240 demaps the constellation points output from the Fouriertransformer 230 or the STBC decoder to bit streams. If LDPC encoding isused, the demapper 240 may further perform LDPC tone demapping beforeconstellation demapping. The deinterleaver 250 deinterleaves the bits ofeach stream output from the demapper 240. Deinterleaving may be appliedonly when BCC encoding is used.

When MIMO or MU-MIMO is used, the receiving signal processing unit 200may use a plurality of demappers 240 and a plurality of deinterleavers250 corresponding to the number of spatial streams. In this case, thereceiving signal processing unit 200 may further include a streamdeparser for combining the streams output from the deinterleavers 250.

The decoder 260 decodes the streams output from the deinterleaver 250 orthe stream deparser. For example, the decoder 260 may be an FEC decoder.The FEC decoder may include a BCC decoder or an LDPC decoder. Thereceiving signal processing unit 200 may further include a descramblerfor descrambling the decoded data. If BCC decoding is used in thedecoder 260, the receiving signal processing unit 200 may furtherinclude an encoder deparser for multiplexing the data decoded by aplurality of BCC decoders. If LDPC decoding is used in the decoder 260,the receiving signal processing unit 200 may not use the encoderdeparser.

FIG. 16 is a timing diagram providing an example of the Carrier SenseMultiple Access/Collision Avoidance (CSMA/CA) transmission procedure,according to some embodiments. In the illustrated example, STA1 is atransmit WLAN device for transmitting data, STA2 is a receive WLANdevice for receiving the data, and STA3 is a WLAN device, which may belocated at an area where a frame transmitted from the STA1 and/or aframe transmitted from the STA2 can be received by the WLAN device.

STA1 may determine whether the channel is busy by carrier sensing. TheSTA1 may determine the channel occupation based on a quality of thesignal on the channel or correlation of signals in the channel, or maydetermine the channel occupation by using a network allocation vector(NAV) timer.

When determining that the channel is not used by other devices duringDIFS (that is, the channel is idle), STA1 may transmit an RTS frame toSTA2 after performing backoff. Upon receiving the RTS frame, STA2 maytransmit a CTS frame as a response of the CTS frame after SIFS. WhenSTA3 receives the RTS frame, it may set the NAV timer for a transmissionduration of subsequently transmitted frames (for example, a duration ofSIFS+CTS frame duration+SIFS+data frame duration+SIFS+ACK frameduration) by using duration information included in the RTS frame. WhenSTA3 receives the CTS frame, it may set the NAV timer for a transmissionduration of subsequently transmitted frames (for example, a duration ofSIFS+data frame duration+SIFS+ACK frame duration) by using durationinformation included in the RTS frame. Upon receiving a new frame beforethe NAV timer expires, STA3 may update the NAV timer by using durationinformation included in the new frame. STA3 does not attempt to accessthe channel until the NAV timer expires.

When STA1 receives the CTS frame from the STA2, it may transmit a dataframe to the STA2 after SIFS elapses from a time when the CTS frame hasbeen completely received. Upon successfully receiving the data frame,the STA2 may transmit an ACK frame as a response of the data frame afterSIFS elapses.

When the NAV timer expires, STA3 may determine whether the channel isbusy through the use of carrier sensing techniques. Upon determiningthat the channel is not used by other devices during DIFS and after theNAV timer has expired, STA3 may attempt channel access after acontention window according to random backoff elapses.

The solutions provided herein have been described with reference to awireless LAN system; however, it should be understood that thesesolutions are also applicable to other network environments, such ascellular telecommunication networks, wired networks, and similarcommunication networks.

FIG. 17 is a diagram illustrating a DL MU PPDU and UL MU PPDU exchange,according to some embodiments. In the illustrated example, an APtransmits a DL OFDMA PPDU in a High Efficiency (HE) PPDU format. The HEPPDU format includes a legacy preamble, an HE preamble, and datadestined for each STA. The AP transmits the data for STA1, STA2, STA3,STA4, STA5, STA6, and STA7 through sub-channels of 5 MHz, 5 MHz, 10 MHz,5 MHz, 5 MHz, 5 MHz, and 5 MHz, respectively. In this example, afterSIFS time from receiving the DL OFDMA PPDU, STA1 and STA4 transmitcontrol response frames in a UL OFDMA PPDU in an HE PPDU format (e.g.,through sub-channels of 20 MHz and 20 MHz, respectively).

An embodiment of the invention may be an article of manufacture in whicha non-transitory machine-readable medium (such as microelectronicmemory) has stored thereon instructions which program one or more dataprocessing components (generically referred to here as a “processor”) toperform the operations described above. In other embodiments, some ofthese operations might be performed by specific hardware components thatcontain hardwired logic (e.g., dedicated digital filter blocks and statemachines). Those operations might alternatively be performed by anycombination of programmed data processing components and fixed hardwiredcircuit components.

Some portions of the preceding detailed descriptions have been presentedin terms of algorithms and symbolic representations of operations ondata bits within a computer memory. These algorithmic descriptions andrepresentations are the ways used by those skilled in conferencingtechnology to most effectively convey the substance of their work toothers skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of operations leading to adesired result. The operations are those requiring physicalmanipulations of physical quantities. It should be borne in mind,however, that all of these and similar terms are to be associated withthe appropriate physical quantities and are merely convenient labelsapplied to these quantities. Unless specifically stated otherwise asapparent from the above discussion, it is appreciated that throughoutthe description, discussions utilizing terms such as those set forth inthe claims below, refer to the action and processes of a conferencedevice, or similar electronic computing device, that manipulates andtransforms data represented as physical (electronic) quantities withinthe conference device's registers and memories into other data similarlyrepresented as physical quantities within the conference device'smemories or registers or other such information storage, transmission ordisplay devices.

While the flow diagrams in the figures herein show a particular order ofoperations performed by certain embodiments of the invention, it shouldbe understood that such order is exemplary (e.g., alternativeembodiments may perform the operations in a different order, combinecertain operations, overlap certain operations, etc.).

While the invention has been described in terms of several embodiments,those skilled in the art will recognize that the invention is notlimited to the embodiments described, can be practiced with modificationand alteration within the spirit and scope of the appended claims. Thedescription is thus to be regarded as illustrative instead of limiting.

What is claimed is:
 1. A network device to function as a station (STA)in a Wireless Local Area Network (WLAN), the STA configured toacknowledge a downlink (DL) multi-user (MU) physical layer (PHY)Protocol Data Unit (PPDU) transmitted by an access point (AP),comprising: one or more memories; and one or more processors coupled tothe one or more memories, the one or more processors configured to causethe network device functioning as the STA to perform operationscomprising: receiving the DL MU PPDU; decoding a frame from the DL MUPPDU; determining whether an ACK Policy field of the frame is set to abinary value of ‘01’, wherein the binary value of ‘01’ indicates to theSTA to provide a trigger-based immediate acknowledgement; determiningwhether a trigger information for an uplink (UL) MU transmission hasbeen obtained from the DL MU PPDU; responsive to the determination thatthe ACK Policy field of the frame is set to the binary value of ‘01’ anda determination that the trigger information has been obtained from theDL MU PPDU, transmitting a trigger-based immediate acknowledgement frameto the AP, according to the trigger information; and responsive to thedetermination that the ACK Policy field of the frame is set to thebinary value of ‘01’ and a determination that the trigger informationhas not been obtained from the DL MU PPDU, refraining from transmittingthe trigger-based immediate acknowledgement frame to the AP.
 2. Thenetwork device of claim 1, wherein the binary value of ‘01’ is areserved value for acknowledgement in a Power Save Multi-Poll (PSMP)context.
 3. The network device of claim 2, wherein the ACK Policy fieldset to the binary value of ‘01’ in the PSMP context indicates to the STAthat a response frame to a received frame is allowed but is neither anacknowledgement frame nor any data frame of subtype ContentionFree-Acknowledgement (+CF-Ack) when bit 6 of a frame control field isset to ‘1’.
 4. The network device of claim 3, wherein the ACK Policyfield set to the binary value of ‘01’ in the PSMP context indicates tothe STA that an acknowledgment for a frame received in a PSMP downlinktransmission time (PSMP-DTT) is to be received in a later PSMP uplinktransmission time (PSMP-UTT) when bit 6 of the frame control field isset to ‘0’.
 5. The network device of claim 1, wherein the frame is adata frame.
 6. The network device of claim 1, wherein refraining fromtransmitting the trigger-based immediate acknowledgement framecomprises: waiting for a Block ACK Request frame for the frame; andtransmitting an acknowledgement frame for the frame to the AP inresponse to receiving the Block ACK Request frame.
 7. The network deviceof claim 1, wherein transmitting the trigger-based immediateacknowledgement frame comprises: transmitting the trigger-basedimmediate acknowledgement frame a short inter frame space (SIFS) afterreceiving the DL MU PPDU.
 8. The network device of claim 1, wherein thetrigger information includes information regarding an allocation oftransmission resources for the UL MU transmission, and whereintransmitting the trigger-based immediate acknowledgement framecomprises: transmitting the trigger-based immediate acknowledgementframe by using a transmission resource allocated to the STA.
 9. A methodimplemented by a station (STA) in a Wireless Local Area Network (WLAN)to acknowledge a downlink (DL) multi-user (MU) physical layer (PHY)Protocol Data Unit (PPDU) transmitted by an access point (AP), themethod comprising: receiving the DL MU PPDU; decoding a frame from theDL MU PPDU; determining whether an ACK Policy field of the frame is setto a binary value of ‘01’, wherein the binary value of ‘01’ indicates tothe STA to provide a trigger-based immediate acknowledgement;determining whether a trigger information for an uplink (UL) MUtransmission has been obtained from the DL MU PPDU; responsive to thedetermination that the ACK Policy field of the frame is set to thebinary value of ‘01’ and a determination that the trigger informationhas been obtained from the DL MU PPDU, transmitting a trigger-basedimmediate acknowledgement frame to the AP, according to the triggerinformation; and responsive to the determination that the ACK Policyfield of the frame is set to the binary value of ‘01’ and adetermination that the trigger information has not been obtained fromthe DL MU PPDU, refraining from transmitting the trigger-based immediateacknowledgement frame to the AP.
 10. The method of claim 9, wherein thebinary value of ‘01’ is a reserved value for acknowledgement in a PowerSave Multi-Poll (PSMP) context.
 11. The method of claim 10, wherein theACK Policy field set to the binary value of ‘01’ in the PSMP contextindicates to the STA that a response frame to a received frame isallowed but is neither an acknowledgement frame nor any data frame ofsubtype Contention Free-Acknowledgement (+CF-Ack) when bit 6 of a framecontrol field is set to ‘1’.
 12. The method of claim 11, wherein the ACKPolicy field set to the binary value of ‘01’ in the PSMP contextindicates to the STA that an acknowledgment for a frame received in aPSMP downlink transmission time (PSMP-DTT) is to be received in a laterPSMP uplink transmission time (PSMP-UTT) when bit 6 of the frame controlfield is set to ‘0’.
 13. The method of claim 9, wherein the frame is adata frame.
 14. The method of claim 9, wherein refraining fromtransmitting the trigger-based immediate acknowledgement framecomprises: waiting for a Block ACK Request frame for the frame; andtransmitting an acknowledgement frame for the frame to the AP inresponse to receiving the Block ACK Request frame.
 15. The method ofclaim 9, wherein transmitting the trigger-based immediateacknowledgement frame comprises: transmitting the trigger-basedimmediate acknowledgement frame a short inter frame space (SIFS) afterreceiving the DL MU PPDU.
 16. The method of claim 9, wherein the triggerinformation includes information regarding an allocation of transmissionresources for the UL MU transmission, and wherein transmitting thetrigger-based immediate acknowledgement frame comprises: transmittingthe trigger-based immediate acknowledgement frame by using atransmission resource allocated to the STA.